SEDIMENTOLOGICAL AND MICROMORPHOLOGICAL EXAMINATION OF A LATE DEVENSIAN MULTIPLE DIAMICTON SEQUENCE NEAR MONEYDIE, PERTHSHIRE, EAST-CENTRALSCOTLAND

Re-investigation of a site at Shochie Burn near Moneydie in east-centr al Scotland suggests that earlier interpretations need to be modified. At this site, in the past, two tills were recognized as indicative of two separate ice advances. Previously, this site was known as a strat otype for the Perth Readvance in eastern Scotland. The evidence for a regional readvance is no longer accepted but the two-till problem rema ins unexplained. Present investigations suggest that the two tills are part of a large package of sediments deposited as stacked layers of a subglacial deforming bed that have been tectonized by a very short an d local ice readvance perhaps of the type that occurs as a winter read vance. Sedimentological and micromorphological evidence points to the tills as not being separate but of the same depositional phase undergo ing subglacial deformation and/or local marginal tectonization followi ng subglacial transport in a deforming bed environment resulting in th e incorporation of proximal outwash sediments. The till at Shochie Bur n exhibits evidence, both at the macro-and microscale, of intense defo rmation under high porewater pressures that are attributable to the st rong plasmic microstructures, fold structures, shear zones, Riedel she ars, and of possible submarginal freezing conditions resulting in loca lized brecciation and foliation structure development. This is the fir st site in this area to indicate the presence of subglacial deforming bed conditions followed by marginal glaciotectonism, therefore continu ed research is necessary to establish this modified view of subglacial conditions in this part of Scotland.